Lecture Notes on Spectroscopy and Analytical Chemistry

Flashcards about NMR Spectroscopy

What is spin-spin coupling (J-coupling) in NMR spectroscopy?

The interaction between the magnetic fields of nuclear spins on neighboring atoms, causing splitting of NMR signals into multiple peaks.

What is the J-Coupling Constant (J)?

Measured in Hz, it represents the strength of the spin-spin interaction. It is independent of the external magnetic field strength.

What is the general rule for predicting the number of peaks in a multiplet due to spin-spin coupling?

n + 1 peaks, where n is the number of neighboring equivalent protons.

What are equivalent protons?

Protons that are in identical chemical environments and behave the same way in the magnetic field.

What are non-equivalent protons?

Protons that are in different chemical environments and thus resonate at different frequencies.

How can chemical symmetry be used to determine equivalence of protons?

If protons are interchangeable by a symmetry operation (like rotation or reflection), they are usually equivalent.

What is a shielded proton?

A shielded proton is surrounded by electron density that opposes the external magnetic field, reducing the net field the nucleus 'feels'.

Where does a shielded proton appear on an NMR spectrum?

Appears upfield (to the right, lower ppm, e.g., 0–2 ppm).

What is a deshielded proton?

A deshielded proton has reduced electron density, making it more exposed to the magnetic field.

Where does a deshielded proton appear on an NMR spectrum?

Appears downfield (to the left, higher ppm, e.g., 4–12 ppm).

How does electronegativity affect shielding/deshielding?

Electronegative atoms pull electron density, causing deshielding.

How do pi bonds/aromaticity affect shielding/deshielding?

Induce circulating currents that deshield nearby protons.

What is NMR (Nuclear Magnetic Resonance) spectroscopy?

A technique using a strong magnet and radio waves to determine molecular structure by 'listening' to the tiny magnets inside atoms.

What does the signal recorded by the NMR machine tell us?

It tells us about the atom’s surroundings.

What is a chromophore?

The part of a molecule that absorbs light and is responsible for its color, containing pi or non-bonding electrons.

What is an auxochrome?

A group of atoms that does not absorb light on its own but changes the color and enhances the absorption of a chromophore when attached to it.

What does it mean for a molecule to be chiral?

A molecule that cannot be superimposed on its mirror image.

What is a chiral center (or stereocenter)?

A carbon atom bonded to four different atoms or groups.

What are enantiomers?

Two molecules that are mirror images of each other.

What is the coupling constant (J)?

A number that tells us how strongly two nearby nuclei are interacting in NMR spectroscopy, causing splitting of NMR signals.

What unit is the coupling constant (J) measured in?

Measured in Hertz (Hz).

What is the Zeolite process?

The zeolite process is a water softening method used to remove hardness (mainly calcium (Ca²⁺) and magnesium (Mg²⁺) ions) from hard water.

What is Zeolite?

A natural or synthetic mineral (usually sodium aluminosilicate) with a porous structure and exchangeable sodium ions (Na⁺).

How does Zeolite soften water?

Ca²⁺ and Mg²⁺ ions in hard water are exchanged with Na⁺ ions from the zeolite.

What is the reaction for Zeolite softening process?

Ca²⁺ + Na₂Zeolite → CaZeolite + 2 Na⁺

How to regenerate Zeolite?

Washing it with a concentrated sodium chloride solution (brine).

What is flame photometry?

An analytical technique used to measure the concentration of certain metal ions in a sample by heating the sample in a flame and measuring the emitted light.

What happen during excitation in flame photometry?

The heat from the flame provides energy to the metal ions, causing the electrons to move to a higher energy state (excited state).

What is the role of monochromator in flame photometry?

The emitted light passes through a filter or monochromator to isolate the wavelength corresponding to the ion being measured.

What is cracking in chemistry?

In petroleum refining, it is a process used to break down large, complex hydrocarbons into smaller, more useful molecules.

What is thermal cracking?

Uses heat to break down large hydrocarbons.

What is catalytic cracking?

Uses a catalyst to break down hydrocarbons at lower temperatures.

How is Paracetamol Synthesized?

Acetylation of p-aminophenol using acetic anhydride or acetyl chloride.

What is the first step in synthesizing paracetamol?

Dissolve p-aminophenol in water or alcohol.

What follows the reaction and heating step in synthesizing paracetamol?

Cooling and crystallization.